The production of oil or gas from a subterranean formation may include some amount of water, the source of the water being a water producing zone in communication with an oil or gas region through a fracture, a high-permeability streak or a high-permeability zone, and the like. Controlling the water control can be problematic. One such problem regards shutting off fractures or fissures in carbonate reservoirs without impacting the hydrocarbon production. The fissure or fracture tends to dominate flow (relative to the matrix flow) to a producing well. For example, the flow of hydrocarbons may move from the matrix into the fractures, and then into one or more main fractures that intersect the wellbore. Because of the huge flow potential in a sizable opening, a large fluid solution is utilized to resist extrusion after a well is treated and placed on production. A reservoir may also contain a range of fissures, fractures, and vugs, each of which has the potential to flow. Vugs have both flow potential and large storage capacity, while the capacity of fissures and fractures depend upon width and cementation. Such features cannot be easily mapped, leading to difficulties in designing a plugging treatment.
Existing well treatment solutions addressing these problems are generally referred to as lost circulation material (LCM), lost circulation pills, plugs, gels, cement plugs, formation damage plugs, solids laden plugs, bentonite plugs, and fiber plugs, among other examples. Some solutions include pumping water-reactive materials in a non-aqueous fluid (such as clay, bentonite, organic polymers, and cement) that tends to set when water is encountered. Other solutions include aqueous fluids that set into stiff gels, such as crosslinked, water-soluble, organic polymers, or silicates, aluminum compounds, and other inorganic monomers that gel. Other solutions include resins and other non-aqueous fluids, or slurries of walnut shells, diatomaceous earth, silica flour, and/or other solids in aqueous or non-aqueous carrier fluids that plug indiscriminately. Non-compatible waters that precipitate upon meeting in the reservoir may also be utilized.
Conformance control (also referred to as profile modification) is a type of well treatment solution directed to improve the injection or production profile of a well. Conformance control encompasses procedures that enhance recovery efficiency, such as by reducing the proportion of water produced with the oil or gas. High water production (caused by permeability variations in a subterranean formation) may be addressed by reducing the permeability of a portion of the subterranean formation having high permeability and low oil or gas content.
Presently, oilfield service companies have implemented a number of methods for reducing the permeability of a portion of a subterranean formation. One method (sometimes referred to as permeability blocking) involves injecting a crosslinkable polymer to form a gel within the matrix of the subterranean formation that physically blocks fluid flow through the portion of the formation. Such method either (1) directs the fluid flow around the portion of the formation or (2) induces production from the non-drained portions. As a result, fluid flow is directed through other portions of the subterranean formation having lower permeability or higher oil saturation. The polymer compositions for use in this method are sometimes referred to as crosslinkable polymer compositions.